1. Field of the Invention
This invention relates to a coating composition capable of inhibiting the filiform corrosion which frequently occurs on coated articles of iron, aluminium and magnesium when the articles are used under relative humidity of about 60 to 95%.
2. Description of the Prior Art
The filiform corrosion is one of the typical of corrosion occuring in coated or otherwise decorated containers, furniture, electrical appliances, and automobiles. Efforts are continued to preclude this corrosion. A method which comprises subjecting the surface of a steel plate to a so-called chemical treatment for forming thereon crystals of iron phosphate or zinc phosphate and subsequently applying a coat thereto, and a method which comprises plating the surface of a steel plate with a metal such as zinc, nickel, or chromium which is incapable of causing filiform corrosion and subsequently applying a coat thereto are now in actual use. The former method, however, fails to provide thorough prohibition of filiform corrosion for products intended for use under high humidity, although it provides effective prohibition of filiform corrosion for products intended for use under mild conditions such as in dry room interiors. The latter method provides effective prevention of filiform corrosion only when the plating is effected to an ample thickness. This method, however, poses a problem from the standpoint of saving of resources and production cost and, therefore, has not come to find popular acceptance as an undercoat.